1. Field of the Invention
The present invention relates to a reading apparatus, such as copying machine or a facsimile transmitter, which is provided with a document table, more particularly, to an apparatus which automatically detects the presence or absence of a document and/or the size of a document.
2. Description of the Prior Art
Some of conventional copying machines or facsimile transmitters automatically detect the size of a document in order to copy or transmit the document in accordance with the designated size of copy paper or receiving paper. There are specific arts used for detecting the size of the document like the one disclosed by Japanese Utility Model Publication No. 61-28195 (1986) or Japanese Patent Laid-Open No. 54-83438 (1979) for example.
Of these, the former art detects the size of document by intensity of light received by photoreceptive elements integrated in the document-cover of the document table. The latter art detects the size of document from the side-edge portion of the document by calculating black value of binary signals, i.e., black portion without presence of a document, from the start point of scanning line by image pickup element like line image sensors for example.
However, if a thick document is used, the document cover cannot be closed, leaving some opening which in turn allows entry of external light. This causes photoreceptive element to incorrectly detect the intensity of light and the size of document, thus eventually resulting in the erroneous copying or data-transmission.